Production of pitch



y 1933- G. E. MCCLOSKEY 1,907,078

PRODUCTION OF PITCH Filed Oct. 19, 1928 2 Shets-Sheet l INVENTORATTORNEYS y 1933- G. E. MCCLOSKEY 1,907,078

PRODUCTION OF PITCH Filed Oct. 19, 1928 2 Sheets-Sheet 2 INVENTORATTORNEY5 Patented May 2, '1933 UNITED STATES PATENT OFFICEPENNSYLVANIA, ASSIGNOB TO THE CORPORATION OF N EW JERSEY PRODUCTION OFPITCH Application filed October 1a, 1928. serial no. 313,423

This invention relates to the construction and operation of coaldistillation lants adapted for the production of dehy rated tars andpitches, and includes an electrical precipitator of new design. Theinvention will be described more particularly as applied to a by-productcoke oven battery.

In the ordinary operation of by-product coke ovens the gases produced bythe coking operation pass from the individual ovens through uptake pipesand goose-necks to a collector main common to the ovens of the battery.The foul gases which leave the ovens at high temperature, e. g. 600 to700 C. or higher, are cooled ordinarily as rapidly as possible by theapplication of sprays of ammonia liquor or ammonia liquor and tar in thegoose-necks and collector main. The rapid cooling causes the separatiorrof heavy tar in the collector main." Further cooling is effected in thecross-over main which connects the collector main to the condensingsystem and an additional uantit of tar carrying both heavier and lig teroi s is thus separated. Light 'tar or tarry oil is thrown down in thecondensing system. The collected tars are ordinarily shipped from thecoke-oven plant to a tar distillation plant for distillation andseparation of the oils and the production of pitches of varyinqualities. This redistillation of tar to recover pitches and oilstherefrom involves considerable additional expense.

According to this invention, coal distillation may be carried on in theordinary way and the distillation gases may be collected in the ordinaryway, but they are passed through an electrical precipitator of newdesign in which entrained particles are thrown out of the gasses, andthe heavy tar or pitch thus produced is so treated in the electricalprecipitator that a dehydrated product is obtained directly. On coolingthe cleaned gases-which pass through the precipitator clean oils areobtained directly from the ases. The necessity of distilling tar to prouce such clean oils is thus avoided. By regulating the amount of coolingto which the gases are subjected in the collector main and elsewherebefore they are subjected to the electric discharge in the precipitator,the amount and nature of the oils thrown down in the recipitator and theamount and nature of the clean oils obtained inthe condensers locatedbeyond the precipitator can be controlled. The cooling of the gases inthe collector main may be ac: complished by the application of sprays ofammonia liquor or ammonia liquor and tar thereto, but indiscriminatecooling as heretofore practiced is preferably avoided and the amount ofthe cooling,medium supplied to the collector main is regulated so as toreduce the temperature of the gases to a predetermined extent. This maybe accomplished readily by varying the amount of the cooling mediumsupplied with reference to the temperature and volume of the gasestreated so as to condense only those constituents of the gaseswhich areto be separated both in the collector main and by electricalprecipitation. If the ases pass through the precipitator at a bigtemperature, the higher boiling constituents of the gases pass throughthe precipitator in vapor form and a pitch of higher or lower meltingpoint is precipitated. When the gases are passed through theprecipitator at lower temperature, lower boiling oils are also throwndown in the precipitator and tar is obtained as the product of theprecipitator.

The dew points of the gases for the several constituents carried thereinas vapor are lower than the normal boiling points of these constituentsand by suitable regulation of the temperature of the gases in thecollector main, as by spraying with ammonia liquor or ammonia liquor andtar, it is possible to effect the collection of the desired pitchconstituents in the collector main and in the electrical precipitator,leaving the desired oils in the vapor phase. Thus, by suflicientlylowering the temperature of the gases in the collector main all or anydesired part of the heavy oil constituents can be converted into theliquid phase while the remainder of the oil constituents is still in theform of vapor. To accomplish the intended pur ose the temperature of thegases should e maintained above the dew point of the gases for allconstituents which are to be retained in the gases and carried overthereby after the separation of the pitch therefrom. Some of the tarryor itch constituents do not separate readily om the gases, but as tarfog tend ordinarily to remain in the gas stream. The electricalrecipitator, however, effectively removes t is"tar fog from the gases.By regulating the temperature of the gases so as to condense more orless of the heavy oil with the tarry constituents the consistency andcharacter of the heavy tar or pitch recovered in the precipitator can bevaried to produce directly commercial products of the desired character."Part of the tarr or pitch constituents condensed by the coo ing actionof the ammonia liquor or ammonia liquor and tar separate in thecollector main and a part goes forward as suspended particles in the gasstream. It is that part which remains" sus ended in the gas stream whichis' removed y and recovered" in the electrical precipitator.

The precipitator used may be, for example, the well known Cottrellprecipitator and it should be operated at a temperature such as to avoidthe condensation of the oils which are to be carried over with thegases. Consequentl the electrical precipitator should be disposedpreferabl closely adjacent to the collector main an the gases carryingthe pitch constituents should be delivered directly thereto. Theelectrical precipitator may be insulated advantageously to prevent lossof heat from the gases. This is particularly desirable if the product tobe recovered is a relatively high melting point pitch requiring themaintenance of the gases at high temperature to avoid dilution of thepitch with oil constituents.

Although the temperature at which the electrical precipitator isoperated is above the dew point of water, some water may nevertheless becarried over in the form of spray from the collector main and the watermay be present in the form of liquid particles in the electricalprecipitator because the limited time of contact with the gases preventsevaporation of the water. In this case the removal of water in theliquid phase will be efiected by the electrical discharge in theelectrical precipitator and the water will be carried down therein withthe heavy tar or pitch constituents, thus producing a product containinga proportion of water which is undesirable.

The gases in the electrical precipitator may also contain drops of waterproduced by local cooling of those gases near the walls of the mainsthrough which the gases pass or the tubes of the precipitator. AAlthough the average temperature of the gases passing through theprecipitator may be above the dew point of the gases for water, drops ofwater ma form in any portion of the gases which is cooled, e. g. bycontact with a cold surface, and such drops may not have sufiicient timeto blend with the hotter gases and be vaporized thereby before the usesenter the electrical precipitator. Such rop. lets of water are separatedfrom the gases in the precipitator together with the pitch or heavy tar.

According to this invention, water from any source whatever which ispresent in the gases in the li uid phase and is separated from the gases1n the electrical precipitator, is returned to the gases by dehydrationof the heavy tar or pitch thrown down in the precipitator. Any gases orhydrocarbon vapors which are evolved during the dehydration of the heavytar or pitch are added to the gases leaving the precipitator. There isno loss of hydrocarbons from the system during the dehydration.

The heat employed in the dehydration may be supplied. to the pitch ortar in various ways. Advantageously, the dehydration is effected by theprovision of heating means such as a steam coil in the bottom of theprecipitator through which steam under pressure and at a suitabletemperature, for example, approximately 150 C. can be conducted for thepurpose of heating the heavy tar or pitch in the precipitator andevaporating the water therefrom.

The amount of steam required for this purpose is relatively limitedbecause only a small amount of water in liquid phase will normally becarried into the precipitator from the collector main. Thus, in a planthaving sixty ovens and producing a total of about 10,000 gallons of tarper day by the ordinary methods of operation, the amount of pitch with amelting point of 105 F. obtained directly, may not exceed 5,000 gallonscarrying approximately 0.7% of water. The operation of such a plantwould require not to exceed 650 pounds of steam per day to dehydrate thepitch. The amount of steam. required would vary, of

course, depending upon the amount of pitch produced and the proportionof water normally contained therein as the pitch is separated in theprecipitator.

The heating of the tar or pitch in the precipitator can be effected inother ways as by the introduction of other hot gases such as flue gasesor by the use of other heating media. The apparatus employed for heatingmay be modified to meet the requirements of the particular heatingmedia, but the heating should preferably be effected in the bottom ofthe precipitator so that the water is removed from the tar or pitch asthe latter is recovered and so that the vapors, including water andvolatile oil constituents, separated from the product, will be carriedthrough the precipitator and recovered in the condensers.

The operation of an electrical precipitator as commonly used consists inpassing the gas to be treated between electrodes whose difference inelectrical potential is 'very great. Experience has shown that it isbest to use a' rectified alternating current. The alternating current(the primary) is sent through a step-up transformer to produce a highpotential current (the secondary) which is then rectified to anintermittent uni-directional current, for example, by means of a rotaryconverter. The rectified current is delivered from the converter to theelectrical precipitator at practically the potential at which it leavesthe transformer.

The electrical precipitator consists commonly of a group of verticalpipes with a wire or rod in the centre of each, the pipes beingconnected to proper headers for the introduction and discharge of thegases. The pipes generally constitute the positive electrodes and thewires or rods the negative electrodes. The size of the pipes may vary,but in general pipes of less than six inches in diameter are not used.Electrical precipitators with pipes six inches in diameter usingsecondary .voltages from 35,000 to 50,000 volts are satisfactory for thepurposes of this invention; It is generally best to operate with maximumpotential diiference (secondary current) between the electrodes, thismaximum being just below the break-down voltage at which arcing occurs.

The eificiency of the cleaning is depend ent upon several variables.Satisfactory cleaning of the gas may be accomplished if the time oftreatment is of the order of one second, although this time may bevaried widely depending upon the character of the oil to be recoveredfrom the gases leaving the precipitator. In working with tubes nine feetlong and six inches in diameter, for example, an oil substantially freefrom all tarry constituents has been obtained with a time of treatmentof from one and one-half to two seconds, that is to say, with a gasvelocity of from 6 to 4.5 feet per second. This has given an efiiciencyof cleaning of approximately ninetynine percent. If it is desired tocollect oils containing small amounts of tar shorter treatment may beused, for example, a treatment of from 0.5 to one second, that is tosay, with a velocity of from 18 to 9- feet per second.

From the electrical precipitator the gases carrying the condensable oilvapors can be conducted through suitable condensing apparatus includingcoolers, scrubbers, fractional condensers, fractionating columns, etc.designed to reduce the temperature of the gases and to cause the searation of oils therefrom. One total oil action can Electricalprecipitators of the type employed for the separation of the tar orpitch from the gases may be employed to separate the condensed oilvapors by passing the gases through such preci itators at predeterminedtemperatures. llhe condensed constituents can be separated eifectivelyand sharp cuts of oil can be obtained. The gases after successivecondensations accompanied by separation of the oil constituents can beconducted through the usual equipment provided for the purpose ofcooling the gases and of recovering other valuable constituents such asammonia and light oils thereom. It will be understood that in thepractice of the present invention the cooling of the gases in thecollector main will be regulated by supplying more or less ammonialiquor or other cooling agent thereto for the purpose of determining thecharacter of the tar or pitch which may be separated in the electricalprecipitator and that by such regulation the amount of tar and oilconstituents which are condensed in the collector main and separated inthe electrical precipitator may be regulated to produce tar or pitchhaving different melting points and other characteristics. Where veryclose regulation is desired it may be of advantage to insulate thecollector main and the cross-over main up to the electricalprecipitator.

The tars and pitches recovered may be employed for the purposes forwhich similar products produced by the ordinary methods are used, themelting point of the particular product being adjusted by the regulationof the cooling in the collector main as hereinbefore described. The freecarbon content of the products will in general be lower than that ofcorresponding products produced in the ordinary way. The invention maybe applied to existing coke-oven plants without any considerablemodification thereof except for the addition of the electricalprecipitator and the provision of fractional condensing apparatus iffractional condensation rather than total condensation as ordinarilypracticed is desired. Fractional condensation is particularfy desirablein the treatment of gases containing clean Vapors because the fractionsrecovered can be utilized for commercial purposes without furtherdistillation or other treatment.

The present invention is applicable to the treatment of coaldistillation gases at all temperatures at which water is carried intoabove the dewpoint of the gases for water.

5 to the accompanying drawin with reference s which show apparatusembodying the invention and a apted for the practice thereof, but it isintended and will be understood that the invention is not limited to thespecific de- It will be further described .10 tails of the apparatus asillustrated in the drawings, in which Fig. 1 is a plan view of a portionof a coke-oven battery illustrating tion of the invention thereto;

Fig. through the collector main and electrical precipitator; and

Fig. '3 is a section through the precipitator.

Referring to the drawings, 5 indicates the battery of ovens which areconnected through uptake pipes and goose-necks 6 to a collector main 7.Spray nozzles 8 and 9 are provided in the goose-necks and collector mainand are connected by pipes 10 to a pump 11 which delivers the coolingmedium, for example, ammonia liquor, to the oose-necks and collectormain from a suita ble source thereof such as a tank 12. The amount ofthe cooling medium thus supplied is regulated as hereinbefore describedto accomplish the desired reduction in temperature of the gases in thecollector main, it being understood that the temperature should bemaintained above the dew points of constituents of the gases which areto pass through the electrical precipitator in the vapor phase.

From the collector main the gases carrying oil vapors and the condensedtarry or pitchy constituents are delivered through a pipe 13 to theelectrical precipitator. The latter comprises a casing 14 enclosing anumber of tubes 15 which are supported in heads 16 and 17 within thecasing. An inlet 18 near the bottom of the casing conimunicates with achamber 19 which is partially separated from the tube section by abattle 20. An outlet 21 permits the escape of the gases from theseparator after the latter have, passed through the tubes.

A plurality of electrodes 22 preferably in the form of metal rods extendthrough the tubes and are supported from a bus-bar 23 located near theupper ends of the tubes. The bus-bar 23 extends at both ends intocasings 24 which enclose insulators 25 upon which the bus-bar issupported. The high tension current lines extend into one of the casings24 and connect with the bus-bar 23, thus supplying the necessary currentfrom any suitable source of uni-directional current under high tension.The casing of the separator is grounded or otherwise connected to thesource of current to complete the applica- 2 is an enlarged verticalsection the circuit. The casing and tubes form the positive electrode,the electrodes connected to the bus-bar being negative. The form andarrangement of the conductors in the circuit can be varied. Thearrangement should be such as to supply high tension uni-directionalcurrent to the electrodes, thereb permitting a substantially continuoussilent discharge between the electrodes and the tubes through which thegases pass.

The gases carrying tar in the form of globules or tar fog together withsolid materials such as carbon, etc. in finely divided form, enter theelectrical precipitator from the collector main and pass through tubesin the precipitator, being subjected therein to the electrical dischargewhich through ionization of the solid and liquid partic es causes themto separate from the gases and condensable vapors. The separated liquidstogether with the solid particles run down the inner walls of the tubesinto the chamber 19 at the bottom of the separator. A steam coil 26 isshown disposed in the chamber 19, supplied with steam through a pipe,27. The condensed steam may be withdrawn through a pipe 28, steam trap29 and drip 30. The tar or pitch thrown out of the gases is thus heatedto the temperature requisite to remove water therefrom and the watervapor together with other vaporizable constituents of the tar or pitchjoins the gas stream and passes through the tubes of the precipitator.The product can be withdrawn through a sealed outlet 31 which maintainsa suitable head in the chamber 19 surrounding the steam coil 26. r

The gases carrying the condensable vapors escape through the outlet 21and are delivered by a pipe 32 to a condenser 33. The condenser may beof any suitable form and in the present instance I have shown acondenser of the ordinary direct or wet type which is employedfrequently in byproduct recovery systems. The gases and vapors arecooled therein by contact with grid surfaces wet by sprays of ammonialiquor, for example, and the resulting condensates are withdrawn througha pipe 34 to a decanter 35 wherein the oils are separated from theammonia liquor. The gases leaving the condenser through pipe 36 aredelivered toan exhauster 37 which maintains the pressure balance in thesystem. The gases may be conducted thence through the usual equipmentfor the recovery of ammonia, light oils, etc.- therefrom. The ammonialiquor which separates in the condenser can be'recirculated to effectthe desired cooling therein and in the collector main and a part thereofcan be treated in the usual manner for the recovery of ammonia.

The present invention permits the direct recovery of heavy tar or pitchfree from water and of clean oil products from cokeoven and other coaldistillation gases and thus avoids the necessity for dehydration anddistillation of tar to produce these products. The desired products arerecovered at a lower cost and in a condition more suitable forcommercial utilization. These and other advantages of the invention maybe attained by the practice of the principles as hereinbefore set forth,it being understood that various changes may be made in the details ofthe operation and in the apparatus as described without departing fromthe invention or sacrificing the advantages thereof.

I claim The method of producing dry tar or pitch which comprises coolinghot coal gasification gases resulting from the gasification of coal toform therein a suspenslon comprising suspended particles of water and oftarry constituents, subjecting the gases to electrical precipitation toremove the suspended particles from the gases, heating the precipitatedmaterial to a temperature of at least 150 C. so as to evaporate thewater therefrom, and returning to the gas stream the water vapor evolvedduring the heating. 4 In testimony whereof I afiix my signature. GREGORYEDWARD McGLOSKEY.

